Compressors



E. A. srALKh-.R` 2,956,732

coMPREssoRs med Feb. 1o. 1954 oct. 1,8, 1,966

IN V EN TOR.

MVM/ff, @j-M,

Unite My invention relates to compressors. The invention provides a new and useful arrangement of the rotor passages bounded by the blades, the rotor hub surface, and the case. These elements govern the variation of passage flow area along the blades. The blades with parallel sides are relatively economical to produce and yet the parallel sides facilitate the exclusion of passage throatsat positions rearward from the noses of the blades so that they are efficient in operating at sonic or supersonic speeds. The use of sonic or supersonic relative fluid speeds provides for a large output of volume and pressure for a given size machine. Thus the compressorhas a'relatively low cost for a given output and this low cost -is further facilitated by the simple and low cost blades of this invention.

This application is a continuation-in-part of my application Serial No. 794,018, filed December 26, 1947, now Patent No. 2,749,027, to which reference is madefor a more complete disclosure and theoretical analysis of the principles of the invention.

An object of the invention is to provide an axial flow compressor which maintains its pressure and eiciency over a wider range of volume iiow per revolution.

Another object is to provide a multistage compressor having a combination of axial flow stages of one type with an axial ow stage of another type.

Still another object of the invention is to'provide an States Patent axial flow machine for increasing the pressure of an elas- Y Other objects will appear from the drawings, specification, and claims. l

The above objects are accomplished by the means illustrated in the accompanying drawings in which:

Figure l is an axial section through an axial flow compressor according to this invention; and

Figure 2 is a fragmentary development of the last rotor showing blades of parallel sides.

When a multi-stage axial flow compressor is operating at a mass flow per revolution less than the optimumV or design value with a back pressure that is relatively low the axial Velocity in the downstream stages may be as much as three times the velocity which would prevail at the optimum or design condition. This is so because the upstream stages do a certain amount of compressing at olf design conditions and the lack of back pressure permits the flow compressed by the upstream stages to stream at greatly increased velocity through the later stages.

This leads to a great change in the direction of the fluid approaching a later rotor or stator with respect to the direction for the optimum operating condition, reducing the angle of attack of the blades and their compressing ability.

Figs. 1 and 2 show a compressor incorporating the fealectively form therotor 48, and the stator stages 51-56 l" rice With their series of blades 66, 70, 74, 7-8, 82, 86 and 100. Fluid enters the inlet 60 and is pumped through the annular or main flow passage 62 to the exit passage 64.

At the upstream end the stator S1 deflects the incoming air by means of the stator blades 66 in the direction of rotation of rotor 41 composed of blades 68. The next stator 52 also deects the lluid in the direction of rotation of rotor 42, but to a less extent, by blades 70. At the third stage the stator 53 deects the iluid substantially axially toward the rotor 43. This stage is comprised of blades 74 and 76.

In the succeeding stages the stator blades deflect the flow with increasing peripheral velocity components against the direction of motion of the rotor blades.

The blades of the fourth stage are 78 and 80 and the blades of the fifth stage are 82 and 84. It is to be noted that in each of these stator stages and in the sixthstator stage the stator blades are curved to give the flow a progressively greater peripheral component in successive downstream stages.

The stator blades 86 for instance in the sixth stage have tail portions directed substantially in the peripheral direction.

The last set of stators takes out the peripheral vcomponent of velocity relative to the case and directs the discharge of uid axially along the passage 64.

The stators are also interconnected by ducts such as 109 to provide for flows of fluid through the blade slats. This construction is similar to that shown in my U.S. VPatent No. 2,344,835, issued March 2l, 1944.

As shown in Fig. l, in the last rotor stage the case 40a diverges from the wall 110 of the rotor 48 as shown at 4012 so that each passage 112 between blades 94 is ex-l panding in cross sectional area until the locality of the blade curvature is reached where the passage area is preferably made to contract slightly so that the flow about the curve is in a favorable pressure gradient. This facilities an efficient ow about the curve but is not essential.

There is also another advantage in the divergence of the hub and case walls. The increase in the cross sectional areas of the rotor passages in the downstream direction slows down the Velocity of flow before the flow is turned by the blade. Hence the appearance of compressibility shock waves is delayed. That is, the peripheral tip speed of the blades can be higher before the shock waveappears in the passages between blades. This means that substantially greater pressure ratios can be obtained from a rotor.

The first shock waves appear at the leading edge of a blade but the critical shock wave which limits the mass flow through the rotor occurs in the passage downstream from the nose of the blade.

If the passages between blades begin to diverge radially opposite the blade noses, the radial expansion can compensate for the peripheral contraction due to the blade thickness. Hence there need not be a throat along the passages between 'blades or at least the throat m-ay be placed far downstream from the inlet of each rotor passage.

Blades 94 have parallel sides as shown by 94a in IFig. 2 providing for fabrica-ting them from sheet metal. Since the thickness can be constant along the blade span the nose radius can be cut by a simple tool passing along the nose o-f the blade. The trailing edge can be made relatively sharp also by a simple tool operation. Thus the blade can be given its proper shape including faired nose and tail portions iat low cost.

By making the last stage with thin blades and relatively sharp noses it can operate with very high fluid velocities without generating shock waves at the nose or in the passage. However in some applications the velocity may become supersonic in the last stage if the back-pressure is reduced suiciently when the rate of rotation of the rotor is near the optimum speed for the compressor as a whole. For this reason the type of rotor shown in the last stage is very advantageous since it can operate even at a supersonic velocity as has been disclosed in my application Serial No. 624,013, led October 23, 1945, now Patent No. 2,648,493, entitled Compressors. Furthermore for a high performance compressor the last stage is preferably made to have a supersonic velocity of approach of the air at the optimum condition of operation. For such a compressor it is important that the angular range of the approach vector should be small to obtain the proper shock waves at the nose of the blades and within the rotor or stator passages. These are provided by this invention.

In an axial ow compressor if the pressure rise is great between inlet and exit for the design condition, then the machine will be much less efficient at a lower delivery, that is at a lower value of the mass of lluid delivered per revolution. The greater the pressure rise, the greater the drop in efficiency at an off-design delivery.

The compressor of this invention using the type of rotor described therein is provided to assuage this undesirable condition and places the axial flow compressor on a more favorable footing with respect to other compressors, such as for instance the centrifugal compressor, than heretofore existed.

As shown in Fig. 2, the blades are placed close together so that they overlap in axial view. Each passage between the blades may be considered as bounded by a leading blade and a following blade (for succinctness in the claims). The normal projection of the leading edge of a following blade on `a leading blade should fall at a point forward of its mid-chord point and substantially ahead of the maximum thickness of the blade section to `assure that a rotor passage throat, if there is one, is a substantial distance downstream from the passage inlet, as remarked earlier. More briefly the leading edge of the following blade may be said to be preferably opposite the mid-chord point of the leading blade or ahead of this point. These proportions insure eflicient operation of the blades in converting the high velocities in the neighborhood of sonic velocities to static pressure.

It will be clear that this invention provides the means of increasing the range of operation of axial ow compressors by providing stators which direct their ow against the adjacent downstream rotor with very high velocity at a value about equal to sonic velocity in the uid appraching the rotor or at somewhat higher than sonic velocity. The ilow leaving the stator, since it is directed against the direction of rotation of the rotor, is defined as making a positive angle with the axis of rotation.

The rotor passages between blades preferably diverge radially but this is not essential for utilizing the positive angle of flow from the stators to a substantial extent to augment the range of mass ilow through the compressor or for utilizing the blade shape for increasing the range of operation. The range of mass ow and the increases in pressure are in part accomplished by having the positive direction of the flow from the stators, by the sonic or high speed nature of the llow, by the shape of the blade sections and by the relatively ilat angles which the rotor blades make with the plane of rotation. Also the blades are adapted by their fair or streamline contours and their close peripheral spacing to handle elastic fluid both at subsonic velocities and at velocities in the neighborhood of sonic values, that is somewhat above sonic as well as subsonic.

The blades have relatively thin blade sections and they overlap in axial View.

The fore portions of the blades are set `on the rotors at small pitch angles, that is angles between the blades and the plane of rotation. See iFig. 2 where the fore portions of blades 94 areset parallel to the velocity vector acting relative to the rotor and are accordingly positioned more along a plane of rotation than along the axis of rotation, that is more nearly parallel to the rotation plane than to the rotation axis.

While I have illustrated a specific form of this invention it is to be understood that I do not intend to limit myself to this exact form but intend to claim my invention broadly as indicated by the appended claims.

Iclaim:

l. In combination in an axial ilow machine for raising the pressure of an elastic fluid flowing therethrough, a case, said machine having an annular passage therethrough bounded by said case with an inlet at the upstream end thereof and an exit at the downstream end thereof, a plurality of rotor and stator stages of rotor and stator blades in alternating arrangement, said plurality of stages including at least one upstream rotor stage for supplying said fluid at an increase in density and at a velocity of supersonic magnitude, and a downstream rotor stage, said rotor stages each comprising a rotor hub and a plurality of blades carried thereon and peripherally spaced thereabout extending across said annular passage dividing said annular passage into a plurality of rotor ow passages lbetween said blades, said annular passage decreasing in radial depth downstream along each of said upstream stages with a depth at the upstream side of said downstream rotor stage substantially less than at the inlet to the first said upstream rotor stage for the ow of uid in said annular passage with increased density and velocity rearward therealong, said rotor ow passages of said downstream stage increasing in cross sectional area in the direction of ow with the cross `sectional areas therealong being at least as large as at the leading edges of its blades and the exit cross Sectional areas of its rotor passages being greater than the inlet cross sectional areas thereof to be effective throughout a subsonic range into a supersonic range of ow of said iluid, said blades of said downstream rotor stage being constructed each with faired nose and tail portions with parallel sides extending therebetween, each said downstream rotor stage blade having substantially convex upper contours and concave lower contours and presenting said concave contours toward the direction of rotation for effecting compressive action on said fluid, and means for applying a force to rotate said downstream rotor stage blades at speeds relative to the ad jacent nid of sonic or greater than sonic speed in the normal condition of operation of said compressor corresponding to uid pressures at substantially maximum values thereof and at substantially the maximum normal rate of rotation of said rotor.

2. In combination in an axial flow machine for raising the pressure of an elastic fluid flowing therethrough, a case, said machine having an annular passage therethrough bounded by said case with an inlet at the upstream end thereof and an exit at the downstream end thereof, a plurality of rotor and stator stages of rotor and stator blades alternated along the axis of said annular passage, said plurality of stages including at least one upstream rotor stage and a downstream rotor stage, said upstream rotor stages being constructed to supply fluid at an increase in density and at a velocity of super sonic magnitude, said rotor stages each comprising a rotor hub and a plurality of blades carried thereon and peripherally spaced thereabout extending across said annular passage dividing said annular passage into a plu rality of rotor flow passages between said blades, said annular passages of each of said upstream rotor stages decreasing in radial depth downstream with a depth at the upstream side of said downstream rotor stage substantially less than `at the inlet to said upstream rotor stage for the flow of said uid in said annular passage with increased density and velocity rearward therealong, said downstream rotor flow passages increasing in cross sectional area downstream therealong with the cross sectional areas therealong being at least `as large as at the leading edges of its blades fand the exit cross sectional areas of said rotor passages being greater than the inlet cross sectional areas thereof to be effective throughout a subsonic range into a supersonic range of ow of said uid, said blades of said downstream rotor stage being constructed each with faired nose and tail portions with parallel sides extending therebetween, each said downstream rotor stage blade having a substantially convex upper contour and la concave lower contour and presenting said concave contours toward the direction of rotation for effecting compressive action on said uid, each said downstream rotor stage blade having the normal projection of its leading edge on the adjacent leading blade at about mid-chord thereof with said blades overlapping in axial view along major portions of the radial lengths thereof, and means for applying a 6 force to notate said downstream rotor stage blades at speeds relative to the adjacent iiuid of sonic or greater than sonic speed in the normal condition of operation of said compressor corresponding to fluid pressures at substantially maximum values thereof and at substantially the maximum normal rate of rotation of said rotor.

References Cited in the ille of this patent UNITED STATES PATENTS 2,597,510 McBride May 20, 1952 2,749,029 Goetzel et al June 5, 1956 FOREIGN PATENTS 368,601 Great Britain r Mar. 10, 51932 385,795 Great Britain Jian. 5, 1933 `892,412 France Ian. 7, 1944 1,060,376 France Nov. 18, 1953 

